Protection sheet for coating film

ABSTRACT

Provided is a protective sheet for a coating layer comprising a substrate sheet and provided thereon a pressure-sensitive adhesive layer, which can be applied as well to a coated surface insufficiently cured immediately after dried, and the pressure-sensitive adhesive layer described above comprises an addition reaction type silicone-based pressure-sensitive adhesive.

TECHNICAL FIELD

The present invention relates to a protective sheet for a coating layer,more specifically to a protective sheet for a coating layer which doesnot allow coating layers applied on automotive bodies and parts ofautomobiles to change in quality or discolor and which is excellent in astripping property after adhered for a long period of time.

The protective sheet for a coating layer according to the presentinvention is a protective sheet capable of being applied as well to acoating layer of a urethane-based coating material in which a smallamount of a solvent remains due to insufficient drying and which isinsufficiently cured after drying, and it is particularly useful as aprotective sheet for coated plastic-made parts such as bumpers and thelike.

BACKGROUND ART

When transporting cars, brought about are the inconveniences that thecoating layers of car bodies and parts become lusterless, discolored anddamaged due to suspended matters such as dirts and dusts, rain, grasspollen and the like, colliding matters such as sands and the like andcontact by workers. In order to prevent such inconveniences, wax-basedmaterials are applied on the coating layers of car bodies and parts ofautomobiles, or protective sheets are adhered thereon.

However, in heating and curing coating layers applied on car bodies andparts, the curing reaction of the coating layers does not sufficientlyproceed in a certain case even after passing through a drying furnace.

Among them, in the case of a bumper which is one of parts forautomobiles, synthetic resin-made bumpers have come to be used in placeof conventional metal-made ones in order to reduce a weight thereof, andthe above synthetic resin-made bumpers are usually coated in order toimprove its appearance. In the case of the above synthetic resin-madebumpers, protective sheets are adhered thereon as well in order toprevent the inconveniences described above.

However, in heating and curing coating layers applied on syntheticresin-made bumpers, the curing temperature can not be elevated in orderto avoid adverse affections such as deterioration and deformation of theresin. Accordingly, the coating layers on the coated resin-made bumpersare insufficiently dried even after passing through a drying furnace,and therefore a small amount of the solvent remains or the curingreaction does not sufficiently proceed in a certain case.

When adhering a protective sheet on a coating layer in such state,brought about are problems such as “stepping (the phenomenon thatdeformations brought about by fine wrinkles and lifting produced on thesheet in adhering the protective sheet are transferred onto the coatinglayer, whereby the coating layer is deformed)”, “whitening (thephenomenon that deviation is caused in the composition of the coatinglayer due to affinity thereof with a pressure-sensitive adhesive layerof the sheet and that the coating layer looks white when stripping thesheet)” and “adhesive deposit (the phenomenon that thepressure-sensitive adhesive layer is partially transferred onto thecoating layer when stripping the sheet)”.

Proposed as a protective sheet for a coating layer are a sheet preparedby providing a layer of a polyisobutylene-based pressure-sensitiveadhesive on a substrate for supporting (for example, a Patent Document1), a sheet prepared by providing a layer of a pressure-sensitiveadhesive comprising butyl rubber or a styrene-ethylene-butylene-styreneblock copolymer on a substrate for supporting (for example, a PatentDocument 2), a sheet prepared by providing a layer of a compositionobtained by mixing a polyisobutylene-based pressure-sensitive adhesivewith a small amount of an acrylic-based pressure-sensitive adhesive on asubstrate for supporting (for example, a Patent Document 3), a sheetprepared by providing a layer of a composition obtained by blending anacrylic-based pressure-sensitive adhesive with a multifunctionalisocyanate compound on a substrate for supporting (for example, a PatentDocument 4), a sheet prepared by providing an ethylene-vinylacetate-glycidyl methacrylate copolymer on a substrate for supporting(for example, a Patent Document 5) and a sheet prepared by providing apressure-sensitive adhesive layer obtained by photo-curing a resincomprising a principal component of an ionomer obtained by subjecting anethylene-methacrylic acid copolymer to intermolecular bonding with metalions on a substrate for supporting (for example, a Patent Document 6).

However, the performances of the protective sheets for a coating layerwhich have the pressure-sensitive adhesive layers described above arenot still satisfactory.

Patent Document 1: U.S. Pat. No. 2,701,020Patent Document 2: U.S. Pat. No. 3,668,322Patent Document 3: U.S. Pat. No. 2,832,565Patent Document 4: U.S. Pat. No. 3,342,977

Patent Document 5: JP 1998-121002A Patent Document 6: JP 1998-121010ADISCLOSURE OF THE INVENTION

In light of the situation described above, an object of the presentinvention is to solve the problems described above in a protective sheetfor a coating layer by using a pressure-sensitive adhesive componenttotally different from the various pressure-sensitive adhesivecomponents described above which have so far been used.

Intensive researches repeated by the present inventor have resulted infinding that the above object can be achieved by using a protectivesheet prepared by applying a pressure-sensitive adhesive layercomprising an addition reaction type silicone-based on a substratesheet, and thus the present inventor has completed the presentinvention.

That is, the present invention provides the following items (1) to (7):

(1) a protective sheet for a coating layer comprising a substrate sheetand provided thereon a pressure-sensitive adhesive layer, wherein thepressure-sensitive adhesive layer comprises an addition reaction typesilicone-based pressure-sensitive adhesive,(2) the protective sheet as described in the above item (1), wherein theaddition reaction type silicone-based pressure-sensitive adhesivefurther contains a curing catalyst,(3) the protective sheet as described in the above item (1) or (2),wherein the curing catalyst is a platinum-based catalyst,(4) the protective sheet as described in the above item (1) or (2),wherein the substrate sheet is a polyethylene terephthalate sheet,(5) the protective sheet as described in the above item (1) or (2),wherein the pressure-sensitive adhesive layer is cross-linked by heatingor irradiating with an active energy beam,(6) the protective sheet as described in the above item (1) or (2),wherein it is a protective sheet for a coating layer which is applied oncars and(7) the protective sheet as described in the above item (1) or (2),wherein it is a protective sheet for a urethane-based coating layerwhich is applied on resin-made bumpers.

According to the present invention, capable of being provided is aprotective sheet for a coating layer which is less liable to allowcoating layers applied on car bodies and parts of automobiles to changein quality or discolor and which is excellent in a stripping propertyafter adhered for a long period of time. In particular, it is useful asa protective sheet for coating layers in which a small amount of asolvent remains due to insufficient drying immediately after drying inplastic-made parts such as coated bumpers and the like and which areinsufficiently cured.

BEST MODE FOR CARRYING OUT THE INVENTION

An addition reaction type silicone-based adhesive which is provided onthe protective sheet for a coating layer according to the presentinvention shall be explained. The addition reaction type silicone-basedadhesive comprises a base resin and a cross-linking agent.

The addition reaction type silicone-based pressure-sensitive adhesive inthe present invention has the advantage that it can be used after onlyprimary curing at low temperatures and does not require secondary curingat high temperatures.

In this regard, conventional peroxide curing type silicone-basedadhesives require secondary curing at a high temperature of 150° C. orhigher.

Accordingly, it becomes possible to produce a protective sheet atrelatively low temperature in the present invention and is excellent inan economical efficiency of energy, and it becomes possible as well toproduce a protective sheet using a substrate sheet having a relativelylow heat resistance. Further, by-products are not produced in curing asis the case with peroxide curing type silicone-based pressure-sensitiveadhesives, and therefore problems of odor and corrosion are not broughtabout.

The addition reaction type silicone-based pressure-sensitive adhesive inthe present invention has a low adhesive strength as compared with thoseof conventional peroxide curing type silicone-based pressure-sensitiveadhesives, and therefore it has the preferred characteristic that itdoes not exert an adverse affection on the coating layer surface whenpeeled after finishing use of the protective sheet.

The addition reaction type silicone-based pressure-sensitive adhesive inthe present invention comprises usually a base resin comprising amixture of a silicone resin component and a silicone rubber component, ahydrosilyl group (SiH)—containing cross-linking agent and a curingcatalyst which is used if necessary.

Among them, the silicone resin component is an organopolysiloxane havinga reticulate structure which is obtained by hydrolyzing anorganochlorosilane or an organoalkoxysilane and then subjecting it todehydration condensation reaction. The silicone rubber component is adiorganopolysiloxane having a straight chain structure. The organo groupincludes methyl, ethyl, propyl, butyl, phenyl and the like in both casesof the silicone resin component and the silicone rubber component. Theorgano groups described above are partially substituted with anunsaturated group such as a vinyl group, a hexenyl group, an allylgroup, a butenyl group, a pentenyl group, an octenyl group, a(meth)acryloyl group, a (meth)acryloylmethyl group, a(meth)acryloylpropyl group, a cyclohexenyl group and the like. Thesilicone rubber components having a vinyl group which are readilyavailable in an industrial scale are preferred. In the adhesivecontaining the above addition reaction type silicone, cross-linkingproceeds by addition reaction of an unsaturated group with a hydrosilylgroup, and a reticulate structure is formed, whereby apressure-sensitive adhesiveness is developed.

The number of the unsaturated group such as a vinyl group is usually0.05 to 3.0 pieces, preferably 0.1 to 2.5 pieces based on 100 pieces oforgano group. The number of the unsaturated group controlled to 0.05piece or more prevents the reactivity with a hydrosilyl group fromlowering to make curing less liable to proceed and provides thepressure-sensitive adhesive with a suited adhesive strength. On theother hand, the number thereof controlled to 3.0 pieces or less elevatesa cross-linking density of the pressure-sensitive adhesive and increasesan adhesive strength thereof, so that an adverse affection is preventedfrom being exerted on coating layers applied on car bodies and the like.

The diorganopolysiloxane includes, to be specific, KS-3703 (having 0.6piece of vinyl group based on 100 pieces of methyl group) manufacturedby Shin-Etsu Chemical Co., Ltd. and BY23-753 (having 0.1 piece of vinylgroup based on 100 pieces of methyl group) and BY24-162 (having 1.4piece of vinyl group based on 100 pieces of methyl group) eachmanufactured by Dow Corning Toray Co., Ltd. Further, SD4560PSA,SD4570PSA, SD4580PSA, SD4584PSA, SD4585PSA, SD4587L and SD4592PSA eachmanufactured by Dow Corning Toray Co., Ltd. can be used as well.

As described above, the organopolysiloxane which is the silicone resincomponent is used usually in a mixture with the silicone rubbercomponent, and the silicone rubber component includes KS-3800 (having7.6 pieces of vinyl group based on 100 pieces of methyl group)manufactured by Shin-Etsu Chemical Co., Ltd. and BY24-162 (having 1.4piece of vinyl group based on 100 pieces of methyl group), BY24-843(having no unsaturated groups) and SD-7292 (having 5.0 pieces of vinylgroup based on 100 pieces of methyl group) each manufactured by DowCorning Toray Co., Ltd.

The specific examples of the addition reaction type silicone describedabove are described in, for example, JP1998-219229A.

A blending ratio of the silicone resin component to the silicone rubbercomponent is usually 250 parts by mass or less for the latter based on100 parts by mass for the former. The blending ratio controlled to 250parts by mass or less for the latter prevents an adverse affection frombeing exerted on coating layers applied on car bodies and the like.

The cross-linking agent is blended so that the number of hydrogen atomsbonded to a silicon atom is usually 0.5 to 10, preferably 1 to 2.5 basedon one group of an unsaturated group such as a vinyl group in thesilicone resin component and the silicone rubber component. The numberof hydrogen atoms controlled to 0.5 or more prevents reaction of anunsaturated group such as a vinyl group with a hydrosilyl group from notcompletely proceeding to make curing inferior. The number of hydrogenatoms controlled to 10 or less prevents the cross-linking agent fromremaining without reacting to exert an adverse affection on coatinglayers applied on car bodies and the like.

A curing catalyst is preferably blended with the pressure-sensitiveadhesive applied on the protective sheet for a coating layer accordingto the present invention in addition to the addition reaction typesilicone component (comprising the silicone resin component and thesilicone rubber component) and the cross-linking agent each describedabove. The addition reaction type silicone-based adhesive in the presentinvention does not have a functional group such as a silanol grouphaving a reactivity with an isocyanate group, and therefore it can beadhered even when a coating layer is insufficiently cured and does notexert an adverse affection on the coating layer when stripping theprotective sheet.

The above curing catalyst is used in order to accelerate hydrosilylationreaction of an unsaturated group in the silicone resin component and thesilicone rubber component with an Si—H group in the cross-linking agent.

The curing catalyst includes a platinum-based catalysts, that is,chloroplatinic acid, an alcohol solution of chloroplatinic acid,reaction products of chloroplatinic acid with an alcohol solution,reaction products of chloroplatinic acid with olefin compounds, reactionproducts of chloroplatinic acid with vinyl group-containing siloxanecompounds, platinum-olefin complexes, platinum-vinyl group-containingsiloxane complexes, platinum-phosphorus complexes and the like. Thespecific examples of the curing catalysts described above are describedin, for example, JP2006-28311A and JP1998-147758A.

More specifically, they include commercial products such as SRX-212manufactured by Dow Corning Toray Co., Ltd., PL-50T manufactured byShin-Etsu Chemical Co., Ltd. and the like.

An amount to be blended of the curing catalyst is usually 5 to 2000 ppm,preferably 10 to 500 ppm in terms of a platinum content based on thetotal amount of the silicone resin component and the silicone rubbercomponent. An amount to be blended of the curing catalyst controlled to5 ppm or more prevents the curing property from being reduced to resultin a reduction in the cross-linking density, that is, a reduction in thecohesion. On the other hand, an amount to be blended thereof controlledto 2000 ppm or less prevents an increase in the cost and makes itpossible to maintain a stability of the pressure-sensitive adhesivelayer, and it prevents the curing catalyst which is used in excess fromexerting an adverse affection on coating layers applied on car bodiesand the like.

In addition to the components described above, various additives can beadded as optional components to the addition reaction typesilicone-based adhesive in the present invention as long ascharacteristics required to the protective sheet for a coating layer arenot damaged. The additives include non-reactive polyorganosiloxanes suchas dimethylsiloxane and dimethyldiphenylsiloxane, antioxidants of aphenol base and others, light stabilizers of a benzotriazole base, flameretardants of a phosphoric ester base and others, antistatic agents suchas cationic surfactants, inert solvents such as toluene and xylene whichare used in order to reduce a viscosity when applying thepressure-sensitive adhesive, colorants and fillers.

In the addition reaction type silicone-based pressure-sensitive adhesivedescribed above, a pressure-sensitive adhesive strength is developedeven at room temperature by blending the respective components describedabove, but it is preferred from the viewpoint of a stability of thepressure-sensitive adhesive strength to apply the abovepressure-sensitive adhesive on a release sheet or a substrate sheetdescribed later, stick both together and then heat or irradiate it withan active energy beam to accelerate cross-linking reaction of thesilicone resin component with the silicone rubber component by thecross-linking agent.

It is to be noted that the energy beam means beams having an energyquantum among electromagnetic waves and charged particle beams, that is,an active light such as a UV ray or an electron beam. When cross-linkingis carried out by irradiating with an electron beam, aphotopolymerization initiator is not required, but when cross-linking iscarried out by irradiating with an active light such as a UV ray, aphotopolymerization initiator is preferably allowed to be present.

The photopolymerization initiator used when irradiated with a UV rayshall not specifically be restricted, and optional photopolymerizationinitiators suitably selected from photopolymerization initiators whichhave so far been conventionally used for UV ray-curing type resins canbe used. The photopolymerization initiator includes, for example,benzoins, benzophenones, acetophenones, α-hydroxyketones,α-aminoketones, α-diketones, α-diketonedialkylacetals, anthraquinones,thioxanthones and other compounds.

The photopolymerization initiators may be used alone or in combinationof two or more kinds thereof. A use amount thereof is selected in arange of usually 0.01 to 30 parts by mass, preferably 0.05 to 20 partsby mass based on 100 parts by mass of the total amount of the additionreaction type silicone component which is used as a base resin and thecross-linking agent each described above.

The protective sheet for a coating layer having a stable adhesivestrength is obtained by heating or irradiating with an active energybeam for cross-linking.

After applying the pressure-sensitive adhesive on the release sheet, itmay be stuck together with the substrate sheet, or after applying thepressure-sensitive adhesive on the substrate sheet, it may be stucktogether with the release sheet.

Used as the substrate sheet are a polyethylene terephthalate sheet, apolyethylene naphthalate sheet, a polyimide sheet, a polyetherimidesheet, a polyaramide sheet, a polyetherketone sheet, apolyether-etherketone sheet, a polyphenylene sulfide sheet, apoly(4-methylpentene-1) sheet and the like. Polyethylene terephthalateand polyethylene naphthalate are preferred from the viewpoints of a heatresistance, a dimensional stability and an economical efficiency.

A thickness of the substrate sheet is somewhat different depending on amaterial used, and it is usually 5 to 300 μm, preferably 10 to 100 μm.In the case of a polyethylene terephthalate sheet which is one of thepreferred substrate sheets, the thickness is 10 to 50 μm.

The pressure-sensitive adhesive can be applied on the release sheet orthe substrate sheet by a gravure coating method, a bar coating method, aspray coating method, a spin coating method, a roll coating method, adie coating method, a knife coating method, an air knife coating method,a hot melt coating method, a curtain coating method and the like whichare usually carried out.

A thickness of the pressure-sensitive adhesive layer after drying whichis formed on the release sheet or the substrate sheet is usually 1 to 50μm, preferably 5 to 40 μm. Controlling a thickness of thepressure-sensitive adhesive layer to 1 μm or more makes it possible tosecure an adhesive strength and a cohesion (holding power) which arerequired to the protective sheet for a coating layer, and controlling itto 50 μm or less avoids an increase in the cost and prevents thepressure-sensitive adhesive layer from protruding beyond the edges.

The pressure-sensitive adhesive layer is formed on the release sheet orthe substrate sheet to superpose both together, and then it is heated orirradiated with an energy beam as described above to cross-link thesilicone resin component with the silicone rubber component, whereby itcan be provided with a stable adhesive strength.

The heating temperature in accelerating cross-linking by heating isusually 60 to 140° C., preferably 80 to 130° C. Heating at 60° C. orhigher prevents the pressure-sensitive adhesive strength from beingunsatisfactory due to insufficient cross-linking of the silicone resincomponent with the silicone rubber component, and heating at 140° C. orlower prevents thermal shrinkage from being brought about on thesubstrate sheet and prevents the pressure-sensitive adhesivedeterioration and discoloration from taking place.

An accelerating voltage of an electron beam in carrying outcross-linking by irradiating with an electron beam which is one ofactive energy beams is usually 130 to 300 kV, preferably 150 to 250 kV.Irradiation at an accelerating voltage of 130 kV or more makes itpossible to prevent the adhesive strength from being unsatisfactory dueto insufficient cross-linking of the silicone resin component with thesilicone rubber component, and irradiation at an accelerating voltage of300 kV or less makes it possible to prevent the pressure-sensitiveadhesive layer and the substrate sheet from being deteriorated ordiscolored. The preferred range of the beam current is 1 to 100 mA.

A dosage of the electron beam to be irradiated is preferably 1 to 70Mrad, more preferably 2 to 20 Mrad. Irradiation at a dosage of 1 Mrad ormore makes it possible to prevent the pressure-sensitive adhesive layerand the substrate sheet from being deteriorated or discolored andprevent the pressure-sensitive adhesiveness from being unsatisfactorydue to insufficient cross-linking. Irradiation at a dosage of 70 Mrad orless makes it possible to prevent the cohesion from being reduced bydeterioration or discoloration of the pressure-sensitive adhesive layerand prevent the substrate sheet from being deteriorated or shrunk.

A dosage in the case of irradiating with a UV ray is suitably selected.A light quantity thereof is 100 to 500 mJ/cm², and an illuminancethereof is 10 to 500 mW/cm².

Heating and irradiation with an active energy beam are preferablycarried out under nitrogen atmosphere in order to prevent the reactionfrom being disturbed by oxygen.

As described above, the stable adhesive strength is provided by heatingor irradiating with an active energy beam to cross-link the siliconeresin component with the silicone rubber component.

The substrate sheet is preferably subjected to corona dischargetreatment and/or ozone treatment before the substrate sheet issuperposed onto the surface of the pressure-sensitive adhesive layerapplied on the release sheet or before applying the pressure-sensitiveadhesive on the substrate sheet in order to strengthen a closeadhesiveness between the pressure-sensitive adhesive layer and thesubstrate sheet from the viewpoint of preventing the “adhesive deposit”phenomenon that the pressure-sensitive adhesive layer is partiallytransferred onto the coating layer when stripping the protective sheetfor a coating layer according to the present invention from coatedsurfaces of car bodies and parts of automobiles.

Capable of being used as the release sheet are resin films ofpolyethylene terephthalate, polyethylene, polypropylene and the likewhich are coated with a releasing agent such as a fluorine-based resin,a silicone-based resin, a long chain alkyl group-containing carbamateand the like.

A thickness of the release sheet is somewhat different depending on thematerials used, and it is usually 10 to 250 μm, preferably 20 to 200 μm.

EXAMPLES

Hereinafter, the present invention is explained in further details withreference to examples, but the present invention shall by no means berestricted thereto.

Example 1

A polyethylene terephthalate film “PET25T70 manufactured by TorayIndustries, Inc.” having a thickness of 25 μm was used as a substratesheet for the protective sheet, and a polyethylene terephthalate film“SP-PET38YSD manufactured by Lintec Corporation” having a thickness of38 μm which was coated with a fluororesin was used as a release sheet.

Used as the addition reaction type silicone-based adhesive was asolution prepared by diluting with 100 parts by mass of toluene, asolution containing 100 parts by mass of SD4585PSA (addition reactiontype silicone containing a cross-linking agent) manufactured by DowCorning Toray Co., Ltd. and 0.9 part by mass of SRX-212 manufactured byDow Corning Toray Co., Ltd. which was a platinum-based curing catalyst.

The solution described above was applied on the surface of the substratesheet described above by a knife coating method so that a thicknessafter drying was 30 μm and dried at 130° C. for 5 minutes, and then thesubstrate sheet was stuck together with a fluororesin-coated surface ofthe release sheet described above to prepare a protective sheet for acoating layer.

Example 2

The same substrate sheet and release sheet as used in Example 1 wereused to carry out the following procedure.

Used as the addition reaction type silicone-based adhesive was asolution prepared by diluting with 100 parts by mass of toluene, asolution containing 100 parts by mass of SD4585PSA (an addition reactiontype silicone containing a cross-linking agent) manufactured by DowCorning Toray Co., Ltd., 10 parts by mass of SD4587LPSA (an additionreaction type silicone containing a cross-linking agent) manufactured byDow Corning Toray Co., Ltd. and 1 part by mass of SRX-212 manufacturedby Dow Corning Toray Co., Ltd. which was a platinum-based curingcatalyst.

The solution described above was applied on the surface of the substratesheet described above by a knife coating method so that a thicknessafter drying was 30 μm and dried at 130° C. for 5 minutes, and then alayer side which was a pressure-sensitive adhesive layer was irradiatedwith an electron beam at an accelerating voltage of 200 kV, a beamcurrent of 20 mA and a dosage of 5 Mrad under nitrogen atmosphere. Then,the substrate sheet was stuck together with a fluororesin-coated surfaceof the release sheet described above to prepare a protective sheet for acoating layer.

Example 3

A protective sheet for a coating layer was prepared in the same manneras in Example 1, except that a polyethylene terephthalate film “PET25TQ37 manufactured by Toray Industries, Inc.” having a thickness of 25 μmwhich contains a UV absorbent was used as a substrate sheet.

COMPARATIVE EXAMPLE 1

A polyethylene film (trade name: PE Wadatoumei 50ASKAI4, manufactured byJ-Film Corporation) having a thickness of 50 μm which contains anantistatic agent was used as a substrate sheet for the protective sheet,and a polyethylene terephthalate film (SP-PET3801, manufactured byLintec Corporation) having a thickness of 38 μm which was coated with asilicone resin was used as a release sheet.

Used as pressure-sensitive adhesive was a solution prepared by mixing100 parts by mass of an acrylic-based pressure-sensitive adhesiveobtained by diluting a butyl acrylate-acrylic acid copolymer (butylacrylate/acrylic acid mole ratio: 10/1) having a weight averagemolecular weight of 600,000 to 30% by mass with ethyl acetate and 5parts by mass of a 5% by mass ethyl acetate solution of1,3-bis(N,N-diglycidylaminomethyl)cyclohexane as a cross-linking agent.

The above solution was applied on a silicone resin-coated surface of therelease sheet described above by a knife coating method so that athickness after drying was 20 μm and dried at 90° C. for 3 minutes, andthen the release sheet was stuck together with the substrate sheetdescribed above to prepare a protective sheet for comparison.

COMPARATIVE EXAMPLE 2

A protective sheet for comparison was prepared in the same manner as inComparative Example 1, except that used as a pressure-sensitive adhesivewas a solution obtained by diluting a rubber base pressure-sensitiveadhesive comprising a polyisobutylene having a viscosity averagemolecular weight of 800,000 to 30% by mass with toluene and that thecross-linking agent was not used.

The protective sheets obtained in the examples and the comparativeexamples described above were used to carry out the following tests, andthe results obtained are shown in Table 1.

<Evaluated Items and Methods for Evaluating>

A double liquid type polyurethane-based top coating material forautomobiles (prepared by mixing 100 parts by mass of Rock Multi TopClear SF-150-5150 with 50 parts by mass of Rock Multi Top Clear S curingagent standard 150-5120 each manufactured by Rock Paint Co., Ltd.) wassprayed in a thickness of about 1 μm on a plate of a polyolefin basethermosetting elastomer on which an electrodepositing primer and anintermediate coating material were applied. It was dried at 60° C. for10 minutes and left standing at room temperature for 30 minutes, andthen the respective protective sheets obtained in the examples and thecomparative examples which were cut into a tape shape were adhered onthe coating layer. The sheets of a tape shape which were adhered on thecoated surfaces with wrinkled parts were left standing at roomtemperature for 24 hours and then peeled, and the states of the coatinglayer were visually observed to evaluate the respective characteristicsaccording to the following criteria.

(1) Stepping of a Wrinkle Part

◯: Step can not be confirmed

Δ: Step can be confirmed, and a vertical interval of stepping is 0.3 to1 μm

X: Step can be confirmed, and a vertical interval of stepping is 1 μm ormore

(2) Boundary Between a Sheet-Adhered Part and a No Adhered Part

◯: Boundary can not be confirmed.

Δ: Boundary can slightly be confirmed.

X: Boundary can clearly be confirmed.

(3) Whitening of an Adhesive Contact Surface

◯: Whitening can not be confirmed.

Δ: Whitening can be confirmed but can not be confirmed after leftstanding outdoors for one week.

X: Whitening can be confirmed and can be still confirmed even after leftstanding outdoors for one week.

(4) Adhesive Deposit

◯: Adhesive deposit can not be confirmed on the coated surface.

Δ: Adhesive deposit can slightly be confirmed on the coated surface.

X: Adhesive deposit can notably be confirmed on the coated surface.

TABLE 1 Comparative Examples Examples 1 2 3 1 2 Stepping of wrinkle part◯ ◯ ◯ X Δ Boundary between sheet- ◯ ◯ ◯ X Δ adhered part and no adheredpart Whitening of adhesive ◯ ◯ ◯ X Δ contact surface Adhesive deposit ◯◯ ◯ X Δ

As apparent from the results shown in Table 1, it can be found that theprotective sheets for a coating layer according to the present inventionobtained in the examples are excellent in all characteristics ascompared with those of the protective sheets obtained in the comparativeexamples.

INDUSTRIAL APPLICABILITY

The protective sheet for a coating layer according to the presentinvention can be applied as well to a coating layer of a urethane-basedcoating material which is insufficiently cured, and in particular, itcan suitably be used as a protective sheet for coated plastic-made partssuch as bumpers and the like.

1. A protective sheet for a coating layer comprising a substrate sheetand provided thereon a pressure-sensitive adhesive layer, wherein thepressure-sensitive adhesive layer comprises an addition reaction typesilicone-based pressure-sensitive adhesive.
 2. The protective sheet asclaimed in claim 1, wherein the addition reaction type silicone-basedpressure-sensitive adhesive further comprises a curing catalyst.
 3. Theprotective sheet as claimed in claim 2, wherein the curing catalyst is aplatinum-based catalyst.
 4. The protective sheet as claimed in claim 1,wherein the substrate sheet is a polyethylene terephthalate sheet. 5.The protective sheet as claimed in claim 1, wherein thepressure-sensitive adhesive layer is cross-linked by heating orirradiating with an active energy beam.
 6. The protective sheet asclaimed in claim 1, wherein a said protective sheet for a coating layeris applied on cars.
 7. The protective sheet as claimed in claim 1,wherein a said protective sheet for a urethane-based coating layer isapplied on resin-made bumpers.
 8. The protective sheet as claimed inclaim 2, wherein the substrate sheet is a polyethylene terephthalatesheet.
 9. The protective sheet as claimed in claim 2, wherein thepressure-sensitive adhesive layer is cross-linked by heating orirradiating with an active energy beam.
 10. The protective sheet asclaimed in claim 2, wherein said protective sheet for a coating layer isapplied on cars.
 11. The protective sheet as claimed in claim 2, whereinsaid protective sheet for a urethane-based coating layer is applied onresin-made bumpers.